This invention in general relates to navigation technology. Further this invention pertains to a Global Positioning System (GPS). More particularly this invention relates to a Global Positioning System receiver.
Global Positioning System receivers are primarily used for navigation purposes. The system generates a position fix by way of outputs, position, speed and other vital navigation information. The receiver is equipped with an antenna and a hardware unit. The hardware unit comprises a radio frequency (RF) down converter, correlator and a navigation processor. The receiver receives satellite signals from the antenna, down converts the signal in the RF down converter and processes the signal in the correlator. The measurement and correlation values from the correlator are transmitted to a navigation processor, for example a Digital Signal Processor or micro controller for further processing. The position and other navigation information is computed in the navigation processor and transmitted in a standard format which can be used by the system integrators to develop various applications around these Global Positioning System receivers like fleet management system, and traffic telematics.
This invention is directed to an improved 12 channel and single frequency coarse acquisition (C/A) code Global Positioning System receiver. By virtue of the invention, the receiver core is realized around a single programmable fixed-point Digital Signal Processor (DSP) microcomputer. The receiver is based on a unique Soft-Correlator architecture, which allows the complete Global Positioning System signal processing as well as navigation processing functions to be implemented on a single programmable fixed point DSP. This flexible implementation lends itself for interfacing with any standard RF front end. The receiver has all the advantages associated with a software requirement, such as scalability, and upgradability. The low cost, high performance DSP microcomputer totally eliminates the necessity of a micro controller, usually required by conventional receiver architectures. The solution includes a Programmatic Interface to the Global Positioning System receiver core, which facilitates the original equipment manufacturers (OEMs) to embed their own applications on the receiver core along with the Global Positioning System function.
The primary object of invention is to develop a complete Global Positioning System receiver core using a single programmable DSP. Using a single programmable DSP was driven by the need to effectively address demands of the emerging applications in the fields of personal navigation, automatic vehicle location (AVL) and traffic telematics. Every new application conceived in these fields invariably involves the integration of Global Positioning System sensor technology with one or more of the technologies from cellular telephone, hands free telephone data modems, speech recognition, speech synthesis, audio/video compression, internet access etc. The Global Positioning System receiver according to the invention has been designed to make seamless integration of multiple technologies feasible without any compromise in performance levels and without the need for customizing silicon.
The conventional Global Positioning System receiver requires the following hardware components for its functioning:                a. Antenna        b. RF down converter        c. Hardware Correlator        d. Navigation processor        
The conventional correlator is used to acquire and track satellite signals. The correlator resides in an Application Specific Integrated Circuit, which is a hardware chip that is customized to the needs of the correlator.
The number of gates required in the Application Specific Integrated Circuit depends on the complexity of the correlator. By way of example, the gates required for a 12 channel correlator is twice the gates required for a 6 channel correlator.
The conventional Global Positioning System receiver uses a specific Radio Frequency down converter for a specific correlator.
The correlator in the conventional Global Positioning System receivers, based on the Application Specific Integrated Circuit has several drawbacks which are listed below:                It requires the usage of 4 hardware units. This makes the Global Positioning System receiver a costly device. The device also consumes a lot of power.        As the complexity of the correlator increases, the cost of the Application Specific Integrated Circuit also increases. Hence the resultant increase in the cost of the Global Positioning System receiver as well as the power consumption.        The performance of the receiver depends mainly on the correlator. Since the correlator resides in an Application Specific Integrated Circuit, which is a customized hardware chip, it is very difficult to implement new signal processing algorithms in the correlator. This feature makes the conventional Global Positioning System receiver inflexible.        The correlator is in hardware and if the RF down converter is changed, it is very difficult to change the correlator. This makes the interface of the correlator with ‘all’ types of RF down converters difficult and contributes to the inflexibility of the system.        